That's a very particular way to frame the few vs the many. If a single macOS user works on ten different projects, should all ten projects add that line, or may things be better off taken out of each project's hands and on that single user?
Not only do people think that, they also think that every pet tool that every pet user might decide to use should also end up cluttering up .gitignores for every project on earth. Worse, these people have created whole templates for this, so they can start a new project with ignores for dozens of tools they don't even use. 9 out of 10 times, this includes a broken ignore for Vim swap files.
I think these people are crazy, and like you suggest, tooling that is particular to you should go in the user's ignore, and tooling particular to the project should go into the repo's ignore.
But I wouldn't want to deny anyone an opportunity to regularly rehash a narrow tribal complaint in the comments on a pull request. Yeesh.
They already answered your situation in their post.
https://en.wikipedia.org/wiki/Narcissism_of_small_difference...
Me, I am pragmatic. I have set this in my local config and I've added it to my repos to be certain. Because it's ten bytes.
I assume that’s why some open source maintainers don’t bother either - if you haven’t even looked at your diff before submitting then why should they?